Even as the U.S. unemployment rate crept downward to 8.1 percent in April, the unemployment rate for 20- to 24-year-olds remained at a stubbornly high 13.2 percent, according to the U.S. Department of Labor.

A college degree can help job seekers immensely, but that piece of paper alone may not be enough to get hired nowadays. Work experience is more important than ever -- and an internship may be the best way to get it.

"Employers want to test-drive their employees before making a formal commitment, and in this job market they're able to do that," says Carl Martellino, executive director of the career center at the University of Southern California.

In 2011, about 42 percent of new hires came through internship programs, according to a survey from the National Association of Colleges and Employers.

"Employers are looking for evidence that the candidate can do the job; the internship offers that evidence," says Marilyn Mackes, the association's executive director.

"We consistently tell students internships are one of the most critical parts of planning for your career," Martellino says.

How internships pay off

An internship helped Mark Silverman go from University of Michigan MBA student to president of the Chicago-based Big Ten Network.

Having lived in Los Angeles and graduated from the University of California, Los Angeles, Silverman was already interested in the entertainment industry. A school event in Michigan encouraged him to look for an internship, which he eventually landed in business development at NBC in New York.

"It was really a great experience," he says. "When it came time to graduate, I was really able to focus my efforts on landing a job in the entertainment industry."

After graduation, Silverman was hired as a financial analyst for The Walt Disney Co. where he played a role in the company's acquisition of another icon -- Miramax.

"In all these experiences, you take away things that you apply later on," he says.

When to start applying for internships

Martellino suggests students start looking for their first summer internship freshman year and get more specialized opportunities each year following. After sophomore year, he recommends students seek an internship in a field they think they might be interested in, and by the summer after junior year, students should try to land an internship at a company they think they'd want to work for following graduation.

While any internship is good to have under your belt, research shows paid internships can offer a wealth of knowledge you might not get as an unpaid intern.

Data collected by the National Association of Colleges and Employers suggest paid interns are more likely to get hired than noninterns and generally earn higher starting salaries. This is because paid interns generally spend more time doing actual work and gaining more real-world experience than unpaid interns, who can often get stuck with clerical tasks, says Mackes.

Internships as recruiting tools

Julia Betts, a corporate communications and investor relations manager, started her decade-long career with National Instruments as an intern.

She says the Austin, Texas, tech company's reputation as one of America's top workplaces initially drew her in.

Beyond getting her foot in the door, starting as an intern gave her the opportunity to try out a couple of different job functions and get to know the company before making a commitment. "Corporate culture is something that you absolutely cannot assess when you're interviewing for a job, but you can when you're an intern," she says.

For companies in competitive, high-growth sectors, internship programs can be especially important recruiting tools.

National Instruments tries hard to hire interns whenever it can, and 99designs, an online marketplace where graphic designers compete for work, is a company whose U.S. operation is staffed in large part by former interns. The Australian company opened a U.S. office in 2008 with one employee. That office has since grown to about 30 employees -- a third of whom were hired through internships.

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